MySQL复制是异步的，也就是说是非同步的过程，它不会校验数据库中数据的一致性，只要SQL语法正确并且没有错误就能成功执行
MASTERtest 12:20:40>create table tab01
-> (id int(10) primary key ,
-> name varchar(20));
Query OK, 0 rows affected (0.03 sec)
MASTERtest 12:21:32>
MASTERtest 12:21:49>show master status;
+----------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+----------------------+----------+--------------+------------------+
| binlog-master.000004 | 338 | | |
+----------------------+----------+--------------+------------------+
1 row in set (0.00 sec)
MASTERtest 12:21:52>
[root@mynode1 mysql]# /service/mysql/bin/mysqlbinlog binlog-master.000004|tail -13
# at 213
#140130 12:21:32 server id 1 end_log_pos 338 Query thread_id=3 exec_time=0 error_code=0
use `test`/*!*/;
SET TIMESTAMP=1391055692/*!*/;
create table tab01
(id int(10) primary key ,
name varchar(20))
/*!*/;
DELIMITER ;
# End of log file
ROLLBACK /* added by mysqlbinlog */;
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/;
可以看到binlog里记录了这条语句，可以通过sql_log_bin参数来控制是否捕获binlog中的操作
MASTERtest 12:25:32>set sql_log_bin=0;
Query OK, 0 rows affected (0.00 sec)
MASTERtest 12:25:37>alter table tab01 add index(name);
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
MASTERtest 12:26:04>set sql_log_bin=1;
Query OK, 0 rows affected (0.00 sec)
MASTERtest 12:26:07>
MASTERtest 12:26:08>show create table tab01\G
*************************** 1. row ***************************
Table: tab01
Create Table: CREATE TABLE `tab01` (
id` int(10) NOT NULL,
name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
[root@mynode1 mysql]# /service/mysql/bin/mysqlbinlog binlog-master.000004
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=1*/;
/*!40019 SET @@session.max_insert_delayed_threads=0*/;
/*!50003 SET @OLD_COMPLETION_TYPE=@@COMPLETION_TYPE,COMPLETION_TYPE=0*/;
DELIMITER /*!*/;
# at 4
#140130 12:08:05 server id 1 end_log_pos 107 Start: binlog v 4, server v 5.5.34-log created 140130 12:08:05 at startup
# Warning: this binlog is either in use or was not closed properly.
ROLLBACK/*!*/;
BINLOG '
JdDpUg8BAAAAZwAAAGsAAAABAAQANS41LjM0LWxvZwAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAl0OlSEzgNAAgAEgAEBAQEEgAAVAAEGggAAAAICAgCAA==
'/*!*/;
# at 107
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#140130 12:13:45 server id 1 end_log_pos 213 Query thread_id=3 exec_time=0 error_code=0
use `tmp`/*!*/;
SET TIMESTAMP=1391055225/*!*/;
SET @@session.pseudo_thread_id=3/*!*/;
SET @@session.foreign_key_checks=1, @@session.sql_auto_is_null=0, @@session.unique_checks=1, @@session.autocommit=1/*!*/;
SET @@session.sql_mode=0/*!*/;
SET @@session.auto_increment_increment=1, @@session.auto_increment_offset=1/*!*/;
/*!\C utf8 *//*!*/;
SET @@session.character_set_client=33,@@session.collation_connection=33,@@session.collation_server=33/*!*/;
SET @@session.lc_time_names=0/*!*/;
SET @@session.collation_database=DEFAULT/*!*/;
create table tab_02 as select * from tab_tmp
/*!*/;
# at 213
#140130 12:21:32 server id 1 end_log_pos 338 Query thread_id=3 exec_time=0 error_code=0
use `test`/*!*/;
SET TIMESTAMP=1391055692/*!*/;
create table tab01
(id int(10) primary key ,
name varchar(20))
/*!*/;
DELIMITER ;
# End of log file
ROLLBACK /* added by mysqlbinlog */;
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/;
[root@mynode1 mysql]#
可以将此DDL语句在slave库执行
SLAVEtest 12:26:39>alter table tab01 add index(name);
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
SLAVEtest 12:27:57>show create table tab01\G
*************************** 1. row ***************************
Table: tab01
Create Table: CREATE TABLE `tab01` (
id` int(10) NOT NULL,
name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
SLAVEtest 12:28:10>
在大型master-slave环境下执行DDL语句时，在每一台slave上手动去执行DDL命令能绕过MySQL数据复制单线程对某些命令的限制